Chemistry 9701/42 — October/November 2021

Cambridge A-Level · A Level Structured Questions · worked solutions for every part, with the mark scheme

questions

100

marks

120

minutes

Topics Chemical Energetics · Equilibria · Electrochemistry · Transition Elements · Introduction to A Level Organic Chemistry · Analytical Techniques · +4 more

Q1Chemical EnergeticsFree sample

Radium is a Group 2 element.

The predicted lattice energy, $\Delta H_{\text{latt}}^{\ominus}$ , of radium sulfide, RaS, is $-2612\text{ kJ mol}^{-1}$ .

(a)

Define $\Delta H_{\text{latt}}^{\ominus}$ .

(b)

Some data relating to radium and sulfur are listed. Select relevant data from this list for use in your answers to parts (b) to (e).

process	value / $\text{kJ mol}^{-1}$
enthalpy change for $\text{Ra(s)} \rightarrow \text{Ra}^{2+}\text{(g)} + 2\text{e}^{-}$	+1619
first ionisation energy of sulfur	+1000
second ionisation energy of sulfur	+2260
first electron affinity of sulfur	-200
second electron affinity of sulfur	+532
enthalpy change for $\frac{1}{8}\text{S}_8\text{(s)} + 2\text{e}^{-} \rightarrow \text{S}^{2-}\text{(g)}$	+555
lattice energy of RaS(s)	-2612

Write an equation for the process corresponding to the second electron affinity of sulfur. Include state symbols.

(c)

Sulfur exists as $\text{S}_8$ molecules in the solid state.

Use the data in this question to calculate the enthalpy change for the reaction $\text{S}_8\text{(s)} \rightarrow 8\text{S(g)}$ .

(d)

Calculate the standard enthalpy change of formation, $\Delta H_{\text{f}}^{\ominus}$ , of radium sulfide.

(e)

(i)

State the two major factors that affect the numerical magnitude of a lattice energy.

(ii)

For each factor you have identified in (e)(i), state whether it tends to make the lattice energy of radium sulfide more or less exothermic than that of sodium chloride.

Explain your answer.

(iii)

The lattice energies of sodium chloride, $\text{NaCl}$ , and radium sulfide, $\text{RaS}$ , are $-771\text{ kJ mol}^{-1}$ and $-2612\text{ kJ mol}^{-1}$ , respectively.

Identify the dominant factor in determining the relative numerical magnitudes of the lattice energies of radium sulfide and sodium chloride.

Explain your answer.

The rest of this paper

9 more questions

Q2Equilibria10M
Q3Electrochemistry · Chemical Energetics9M
Q4Group 2 · Equilibria7M
Q5Transition Elements15M
Q6Transition Elements · Electrochemistry7M
Q7Introduction to A Level Organic Chemistry · Analytical Techniques · Hydrocarbons10M
Q8Nitrogen Compounds · Introduction to A Level Organic Chemistry · Analytical Techniques14M
Q9Nitrogen Compounds10M
Q10Hydroxy Compounds5M

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